The present invention relates to a color spectrum detecting circuit and an image sensing apparatus using the same. Particularly, the color spectrum detection circuit determines whether an input signal is in the range of a color spectrum set in accordance with the color information unaffected (insensitive to) by luminance.
"Contours" is used in the broadcast television camera system art to denote the signal that represents the changes between adjacent picture elements, both vertically and horizontally. A contour correcting circuit emphasizes image sharpness and compensates for response degradation of an image sensing device used in video cameras. For example, in a facial shot, a video camera incorporating such contour correcting circuit would suppress the degree of contour emphasis to prevent every wrinkle and pore on the person's face from being accentuated to highlight the person's aesthetic qualities or to improve the person's aesthetic qualities (i.e., modifying the person's skin tone or flesh tone). This process of suppressing the degree of contour emphasis is referred to as skin tone detail processing.
The skin tone detail processing is explained in conjunction with FIG. 6. Weights are attached to each color difference signals R-Y and B-Y before they are added together to determine hues .phi.U and .phi.L. The result of this addition is supplied to a comparative circuit which compares it to a reference voltage. The comparative circuit generates a gate signal indicative of whether a desired color spectrum AR has been obtained, for example the hatched region in FIG. 6 may represent a skin tone region of the image. Since, the color spectrum detection utilizes luminance sensitive color difference signals R-Y and B-Y, any change in the luminance signal Y, such as a change in the lighting condition or aperture, will alter the signal level of the color difference signals R-Y and B-Y and may lead to incorrect detection of the skin tone region.